U.S. patent number 6,333,082 [Application Number 09/607,959] was granted by the patent office on 2001-12-25 for liquid crystalline (e,e)-butadiene compounds and mixtures and devices containing such compounds.
This patent grant is currently assigned to QinetiQ Ltd. Invention is credited to Warren L Duffy, John W Goodby, Stephen M Kelly.
United States Patent |
6,333,082 |
Duffy , et al. |
December 25, 2001 |
Liquid crystalline (E,E)-butadiene compounds and mixtures and
devices containing such compounds
Abstract
Liquid crystalline compounds useful in super twisted nematic
liquid crystal displays are described and have the formula:
##STR1## wherein n is 1-5; m is 0-5; p is 0, 1 or 2; q is 0, 1 or 2
p+q is less than or equal to 3; A.sub.1, A.sub.2, A.sub.3 are
independently chosen from 1,4-disubstituted benzene,
2,5-disubstituted pyrimidine, 1,5-disubstituted pyridine,
2,6-disubstituted naphthalene which may be laterally substituted
with F, Cl, Br or CN, trans-1,4-disubstituted cyclohexane,
2,5-disubstituted dioxane, 2,5-disubstituted thiophene,
2,5-disubstituted furan, 2,5-disubstituted thiodiazole Z.sub.1 may
be COO, OOC, OCH.sub.2, O; Z.sub.2, Z.sub.3 are independently
chosen from a direct bond, COO, OOC, C.sub.2 H.sub.4, CH.sub.2 O,
OCH.sub.2, C.sub.4 H.sub.8, C.sub.3 H.sub.6 O,
(E)--CH.dbd.CHC.sub.2 H.sub.4, (E)--CH.dbd.CHCH.sub.2 O,
--C.ident.C--; R.sub.1 is alkyl, and may contain up to 20 carbon
atoms and may be branched or a straight chain; provided that at
least one of, A.sub.1, A.sub.2, A.sub.3 is selected from
1,4-disubstituted thiophene.
Inventors: |
Duffy; Warren L (Hull,
GB), Goodby; John W (Hull, GB), Kelly;
Stephen M (Hull, GB) |
Assignee: |
QinetiQ Ltd (London,
GB)
|
Family
ID: |
10800510 |
Appl.
No.: |
09/607,959 |
Filed: |
June 30, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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147886 |
|
6106908 |
|
|
|
Foreign Application Priority Data
|
|
|
|
|
Sep 26, 1996 [GB] |
|
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9620061 |
|
Current U.S.
Class: |
428/1.1;
252/299.61; 252/299.63; 252/299.67; 544/298; 546/339; 546/341;
549/83; 549/80; 549/369; 548/136; 546/340; 544/335; 544/242;
252/299.66 |
Current CPC
Class: |
C07C
255/54 (20130101); C09K 19/32 (20130101); C09K
19/3497 (20130101); C09K 19/3491 (20130101); C09K
19/3469 (20130101); C07C 43/215 (20130101); C07C
255/55 (20130101); C09K 19/3402 (20130101); C09K
19/06 (20130101); C09K 19/3003 (20130101); C07D
319/06 (20130101); C07C 43/225 (20130101); C07C
69/587 (20130101); C09K 19/12 (20130101); C09K
19/3444 (20130101); C09K 2019/3422 (20130101); C09K
2019/0444 (20130101); C09K 2323/00 (20200801); Y10T
428/10 (20150115); C07C 2601/14 (20170501) |
Current International
Class: |
C09K
19/30 (20060101); C09K 19/06 (20060101); C07C
69/587 (20060101); C07C 255/54 (20060101); C07C
69/00 (20060101); C07C 255/00 (20060101); C07C
43/225 (20060101); C07C 43/00 (20060101); C07C
255/55 (20060101); C07D 319/06 (20060101); C07C
43/215 (20060101); C07D 319/00 (20060101); C09K
19/34 (20060101); C09K 19/12 (20060101); C09K
19/32 (20060101); C09K 19/10 (20060101); C09K
019/34 (); C07C 043/188 (); C07D 333/08 (); C07D
213/30 (); C07D 239/02 (); C07D 319/06 () |
Field of
Search: |
;252/299.61,299.63,299.66,299.67 ;428/1.1 ;544/242,298,335
;546/339,340,341 ;548/136 ;549/369,29,61,62,64,80,83
;568/657,667 |
References Cited
[Referenced By]
U.S. Patent Documents
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|
|
5449810 |
September 1995 |
Fujita et al. |
5609791 |
March 1997 |
Fujits et al. |
5662830 |
September 1997 |
Fujita et al. |
5976408 |
November 1999 |
Fujita et al. |
6106908 |
August 2000 |
Duffy et al. |
|
Foreign Patent Documents
Other References
Chemical Abstracts, vol. 125, No. 6, Aug. 5, 1996, Columbus, Ohio,
US; abstract No. 072143, Sakamaki Y et al: Hexadienoyloxybenzoic
acid phenolic compound ester and liquid crystal composition
XP002050221 see abstract & JP 08 059 556 A (Citizen Watch Co
Ltd; Japan) Mar. 5, 1996. .
Chemical Abstracts, vol. 113, No. 14, Oct. 1, 1990, Columbus, Ohio,
US; abstract No. 124013, Shibata T et al:
"2-'4-(2-7-Octadienyloxy)phenyl!-5-alkylpy rimidines as liquid
crystals" XP002050222 see abstract & JP 09 062 865* (Adeka
Argus Chemical Co., Ltd.; Japan). .
Kelly S M: "The effect of the position and configuration of
carbon-carbon double bonds on the mesomorphism of thermotropic,
non-amphiphilic liquid crystals" Liq. Cryst. (LICRE6,02678292):96;
vol. 20 (5); pp. 493-515, Hull Univ.;Sch. Chem.; Hull; HU6 7RX; UK
(GB), XP002050219 see the whole document. .
Kurihara S et al: "Polymerization of liquid crystalline monomers
with diene groups and formation of polymer network with uniaxial
molecular alignment" J. Appl. Polym. Sci. 9JAPNAB, 00218995);96;
vol. 61 (2); pp .279-283, Kumamoto University; Faculty Engineering;
Kumamoto; 860; JAPAN (JP), XP002050220 see the whole
document..
|
Primary Examiner: Wu; Shean C.
Attorney, Agent or Firm: Nixon & Vanderhye
Parent Case Text
This application is a division of Ser. No. 09/147,886, filed Mar.
19, 1999, now U.S. Pat. No. 6,106,908 which is a 35 U.S.C. 371 of
PCT/GB97/02542 filed Sep. 22, 1997.
Claims
What is claimed is:
1. A compound of formula I ##STR24##
wherein
n is 1-5;
mis 0-5;
p is 0, 1 or2;
q is 0, 1 or 2
p+q is less than or equal to 3;
A.sub.1, A.sub.2, A.sub.3 are independently chosen from
1,4-disubstituted benzene, 2,5-disubstituted pyrimidine,
2,5-disubstituted pyridine, 2,6-disubstituted naphthalene which may
be laterally substituted with F, Cl, Br or CN,
trans-4-disubstituted cyclohexane, 2,5-disubstituted dioxane,
2,5-disubstituted thiophene, 2,5-disubstituted furan, and
2,5-disubstituted thiodiazole;
Z.sub.1 may be COO, OOC, OCH.sub.2 or O;
Z.sub.2, Z.sub.3 are independently chosen from a direct bond, COO,
OOC, C.sub.2 H.sub.4, CH.sub.2 O, OCH.sub.2,
C.sub.4 H.sub.8, C.sub.3 H.sub.6 O, (E)--CH.dbd.CHC.sub.2 H.sub.4,
(E)--CH.dbd.CHCH.sub.2 O or --C.ident.C--; and
R.sub.1 is alkyl, and may contain up to 20 carbon atoms and may be
branched or a straight chain;
provided that at least one of, A.sub.1, A.sub.2, A.sub.3 is
selected from 2,5-disubstituted thiophene.
2. A compound according to claim 1 wherein:
n is 1-3;
when Z.sub.1 is 0 m is 1 and when Z.sub.1 is COO m is 0;
p is 0 or 1;
q is 0 or 1;
p+q is 0 or 1;
A.sub.1, A.sub.2, A.sub.3, are 1,4-disubstituted benzene or
trans-1,4-disubstituted cyclohexane; and
Z.sub.2, Z.sub.3 are direct bonds or C.sub.2 H.sub.4.
3. A compound according to claim 2 wherein n+m is.ltoreq.5.
4. A liquid crystal mixture comprising at least one of the
compounds according to claim 1.
5. A liquid crystal mixture according to claim 4 wherein the
mixture is a nematic liquid crystal mixture.
6. A liquid crystal mixture according to claim 4 wherein the
mixture is a cholesteric liquid crystal mixture.
7. A device comprising two spaced cell walls each bearing electrode
structures and treated on at least one facing surface with an
alignment layer, a layer of a liquid crystal material enclosed
between the cell walls, characterised in that it incorporates the
liquid crystal mixture as claimed in claim 4.
8. A device according to claim 7 wherein the device is a twisted
nematic device.
9. A device according to claim 7 wherein the device is a
super-twisted nematic device.
Description
The present invention describes new compounds. In particular it
describes compounds for use in liquid crystal mixtures and in
liquid crystal displays (LCDs) or in applications relating to inter
alia thermography utilising nematic liquid crystal or chiral
nematic liquid crystal mixtures.
BACKGROUND OF THE INVENTION
LCDs, such as multiplexed Twisted Nematic TN-LCDs, Super Twisted
Nematic STN-LCDs, Super Birefringent SBE-LCDs, Electrically
Controlled Birefringence ECB-LCDs, or flexoelectric LCDs are
currently used or being developed for computer monitors, laptop or
notebook computers, portable telephones, personal digital
assistants, etc. The optical, electrical and temporal performance,
e.g., contrast, threshold and driving voltages, and response times,
of such displays depends crucially on the ratios of the elastic
constants (k.sub.33, k.sub.22, k.sub.11) and the cell gap, d.
Currently commercially available nematic mixtures for sophisticated
high-information-content LCDs, such as STN-LCDs, incorporate
trans-1,4-disubstituted-cyclohexyl derivatives with a terminal
alkenyl chain (i.e., incorporating a carbon-carbon double bond)
directly attached to the cyclohexane ring in order to produce the
necessary elastic constant ratios for short response times, high
multiplexing rates and low driving voltages. Such materials are
costly and difficult to synthesise due to the requirement for a
trans configuration of the 1,4-disubstituted cyclohexane ring and
the necessity of synthesising the carbon-carbon double bond
stepwise from this trans-1,4-disubstituted-cyclohexyl intermediate.
If the carbon-carbon double bond is substituted at both carbon
atoms, it must have a trans (E) configuration in order to exhibit
an advantageous combination of elastic constants and to have an
acceptably high nematic-isotropic transition temperature (N-I). The
trans configuration is then generally produced by isomerisation of
the cis (Z) form generated by the preceding Wittig reaction. These
materials exhibit low or intermediate values of birefringence
(.DELTA.n) due to the presence of the saturated cyclohexane rings.
As the ratio d..DELTA.n determines the optical properties of
TN-LCDs and is fixed for driving the LCD in the first or second
minimum, it is clear that higher values of .DELTA.n would allow
smaller cell gaps. As the response time, t.sub.on of TN-LCDs is
inversely proportional to d.sup.2, smaller cell gaps have a
dramatic effect on t.sub.on. Low values of t.sub.on also allow the
use of colour or more shades of colour due to the shorter frame
times.
Liquid crystals with a (E, E)-butadiene chain are known and are
described in, for example W. Meier and K. Markau Z. Phys. Chem. N.
F., (1961), Vol. 28, pp 190, Y. Goto and T. Ogawa, EPA 0 280 902
(1988).
For all the above applications it is not usual for a single
compound to exhibit all of the properties highlighted, normally
mixtures of compounds are used which when mixed together induce the
desired phases and required properties.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view of a matrix multiplex addressed liquid
crystal display;
FIG. 2 is a cross-section of a display such as that of FIG. 1 in a
transmission mode; and
FIG. 3 is a cross-section of a display similar to FIG. 2 operating
in a reflective mode.
DETAILED DESCRIPTION OF THE INVENTION
According to this invention materials are provided of Formula I:
##STR2##
wherein
n may be 1-5;
m may be 1-5;
p may be 0, 1 or 2;
q may be 0, 1 or 2;
p+q is less than or equal to 3;
A.sub.1, A.sub.21 A.sub.3 are independently chosen from
1,4-disubstituted benzene, 2,5-disubstituted pyrimidine,
2,5-disubstituted pyridine, 2,6-disubstituted naphthalene which may
be laterally substituted with F, Cl, Br or CN,
trans-1,4-disubstituted cyclohexane, 2,5-disubstituted dioxane,
2,5-disubstituted thiophene, 2,5-disubstituted furan,
2,5-disubstituted thiodiazole;
Z.sub.1 may be COO, OCC, OCH.sub.2, O;
Z.sub.2, Z.sub.3 are independently chosen from a direct bond, COO,
OOC, C.sub.2 H.sub.4, CH.sub.2 O, OCH.sub.2, C.sub.4 H.sub.8,
C.sub.3 H.sub.6 O, (E)--CH.dbd.CHC.sub.2 H.sub.4,
(E)--CH.dbd.CHCH.sub.2 O, --C.ident.C--;
R.sub.1 may be alkyl, alkoxy, alkenyl, alkenyloxy, alkanoyl,
alkenoyl, F, Cl, Br, CN, OCHF.sub.2, OC.sub.w F.sub.2w+1, NCS or
CH.dbd.C(CN).sub.2, CH.dbd.CF.sub.2, (E)--CH.dbd.CHCl; R.sub.1 may
contain up to 20 carbon atoms and may be branched or a straight
chain and w may be 1-7.
The structural and other preferences are expressed below on the
basis of inter alia desirable liquid crystalline characteristics,
in particular an advantageous combination of elastic constants and
high birefringence in the nematic phase, a wide nematic phase, a
high nematic-isotropic liquid transition temperature and ready
synthesis from commercially available. Starting materials already
incorporating at least one carbon-carbon double bond with the
desired configuration and position.
Preferably n is 1-3;
Preferably when Z.sub.1 is 0 m is 1 and when Z.sub.1 is COO m is
0;
Preferably n+m is.ltoreq.5;
Preferably p is 0 or 1;
Preferably q is 0 or 1;
Preferably p+q is 0 or 1;
Preferably A.sub.1, A.sub.2. A.sub.3, are 1,4-disubstituted benzene
or trans-1,4-disubstituted cyclohexane;
Preferably Z.sub.2, Z.sub.3 are direct bonds or C.sub.2
H.sub.4;
Preferably R.sub.1 is nitrile or alkyl or alkoxy.
Overall preferred structures for formula I are those listed below:
##STR3##
Compounds of formula I can be prepared by various routes. Typically
the ethers can be prepared by the Mitsunobu reaction (Synthesis,
(1981) pp 1) of a phenol with an alka-2,4-dienol in the presence of
triphenyl phosphine, a dehydrating agent, such as diethyl
azodicarboxylate, and a suitable solvent, such as tetrahydrofuran
or N, N'-dimethylformamide. Alternatively they can be synthesised
by alkylation of a secondary alcohol or phenol with the tosylate of
the appropriate alka-2,4-dienol in the presence of a suitable base,
such as potassium tert.-butoxide, and a suitable solvent, such as
tert.-butyl-methyl ether or 1,2-dimethoxyethane (J. Mater. Chem.,
(1994) Vol. 4, pp 1673). The esters can be prepared by
esterification (Angewandte Chemie (1978) Vol. 90, pp 556) of the
appropriate phenol or secondary alcohol with an alkenoic acid in
the presence of 4-(dimethylamino)pyridine, a dehydrating agent,
such as N, N'-dicyclohexylcarbodiimide, and a suitable solvent,
such as dichloromethane or N, N'-dimethylformamide. Alternatively
they can be synthesised by esterification of the appropriate phenol
or secondary alcohol with an alkenoic acid chloride (produced, for
example, from the corresponding alkenoic acid by the action of
thionyl chloride or oxalyl chloride) in the presence of a base,
such as pyridine or triethylamine, and a suitable solvent, such as
toluene or dichloromethane.
In the following examples C signifies the crystalline state, N the
nematic phase, I the isotropic phase, S the smectic phase and
.DELTA.T.sub.NI the temperature range of the nematic phase.
The invention will now be described, by way of example only, with
reference to the following examples.
EXAMPLE 1
Preparation of 4-Cyano-4'-[(E, E)-hexa-2,4-dienyloxy]biphenyl
Triphenylphosphine (0.95 g, 0.0036 mol) was added in small portions
to a solution of (E, E)-hexa-2,4-dien-1-ol (0.40 g, 0.0040 mol),
4-cyano-4'-hydroxybiphenyl (0.71 g, 0.0036 mol)
diethylazodicarboxylate (0.63 g, 0.0036 mol) in dry diethyl ether
(40 cm.sup.3), cooled in an ice bath under an atmosphere of
nitrogen. The reaction mixture was stirred at room temperature
overnight. The solvent was removed under reduced pressure and the
crude product was purified by column chromatography on silica gel
using a 4:1 petroleum (40-60.degree. C.) ether/ethyl acetate
mixture as eluent, followed by recrystallisation from ethanol to
yield 0.19 g (19%) of the pure ether, K 125.degree. C. N-I
152.degree. C.
The following compounds could be obtained analogously:
4-Cyano-4'-[(E, E)-hepta-2,4-dienyloxy]biphenyl.
4-Cyano-4'-[(E, E)-octa-2,4-dienyloxy]biphenyl.
4-Cyano-4'-[(E, E)-nona-2,4-dienyloxy]biphenyl.
4-Cyano-4'-[(E, E)-deca-2,4-dienyloxy]biphenyl.
4-Fluoro-4'-[(E, E)-hexa-2,4-dienyloxy]biphenyl.
4-Chloro-4'-[(E, E)-hexa-2,4-dienyloxy]biphenyl.
4-Bromo-'-[(E, E)-hexa-2,4-dienyloxy]biphenyl.
3,4-Difluoro-4'-[(E, E)-hexa-2,4-dienyloxy]biphenyl.
3,4,5-Trifluoro-4'-[(E, E)-hexa-2,4-dienyloxy]biphenyl.
4-Trifuoromethoxy-4'-[(E, E,)-hexa-2,4-dienyloxy]biphenyl.
4-Trifluoromethyl-4'-[(E, E)-hexa-2,4-dienyloxy]biphenyl.
4-Trifluoroaceto-4'-[(E, E)-hexa-2,4-dienyloxy]biphenyl.
4-Propyl-4'-[(E, E)-hexa-2,4-dienyloxy]biphenyl.
4-Pentyl-4'-[(E, E)-hexa-2,4-dienyloxy]biphenyl, K 119.degree. C.,
S.sub.A -I 136.degree. C.
4-Heptyl-4'-[(E, E)-hexa-2,4-dienyloxy]biphenyl.
4-Methoxy-4'-[(E, E)-hexa-2,4-dienyloxy]biphenyl.
4-Ethoxy-4'-[(E, E)-hexa-2,4-dienyloxy]biphenyl.
4-Propoxy-4'-[(E, E)-hexa-2,4-dienyloxy]biphenyl.
4-Butoxy-4'-[(E, E)-hexa-2,4-dienyloxy]biphenyl.
4-Pentyloxy-4'-[(E, E)-hexa-2,4-dienyloxy]biphenyl.
4-Hexytoxy-4'-[(E, E)-hexa-2,4-dienyloxy]biphenyl.
4-Heptyloxy-4'-[(E, E)-hexa-2,4-dienyloxy]biphenyl.
4-Octyloxy-4'-[(E, E)-hexa-2,4-dienyloxy]biphenyl.
4-Nonyloxy-4'-[(E, E)-hexa-2,4-dienyloxy]biphenyl.
4-Decyloxy-4'-[(E, E)-hexa-2,4-dienyloxy]biphenyl.
4-[(E)-But-2-enyloxy]-4'-[(E, E)-hexa-2,4-dienyloxy]biphenyl.
4,4'-Di-[(E, E)-hexa-2,4-dienyloxy]biphenyl.
1-(trans-4-Pentylcyclohexyl)-4-[(E, E)-hexa-2,4-dienyloxy]benzene,
K 71.degree. C., N-I 107.degree. C.
EXAMPLE 2
Preparation of 4'-Cyanobiphenyl-4-yl (E, E)-hexa-2,4-dienoate
A solution of N, N'-dicyclohexylcarbodiimide (0.87 g, 0.0042 mol)
in dichloromethane (10 cm.sup.3) was added to a solution of (E,
E)-hexa-2,4-dienoic acid (0.47 g, 0.0042 mol),
4-cyano-4'-hydroxybiphenyl (0.67 g, 0.0035 mol),
4-(dimethylamino)pyridine (0.05 g) in dichloromethane (25 cm
.sup.3), cooled in an ice bath (0.degree. C.) under an atmosphere
of nitrogen. The reaction mixture was stirred overnight, filtered
to remove precipitated material and the filtrate was evaporated
down under reduced pressure. The crude product was purified by
column chromatography on silica gel using dichloromethane as
eluent, followed by recrystallisation from a 1:1 ethanol/ethyl
acetate mixture to yield 0.76 9 (76%). K 160.degree. C., N-I
227.degree. C.
The following compounds could be obtained analogously:
4-Cyanophenyl (E, E)-hexa-2,4-dienoate, K 111.degree. C.
4-Cyanophenyl (E, E)-hepta-2,4-dienoate.
4-Cyanophenyl (E, E)-octa-2,4-dienoate.
2-Cyanonaphthyl-6-yl (E, E)-hexa-2,4-dienoate, K 116.degree. C.,
N-I 141.degree. C.
2-Cyanonaphthyl-6-yl (E, E)-hepta-2,4-dienoate.
2-Cyanonaphthyl-6-yl (E, E)-octa-2,4-dienoate.
Biphenyl4-yl (E, E)-hexa-2,4-dienoate, K 110.degree. C., S.sub.A -N
84.degree. C., N-I 92.degree. C.
Biphenyl-4-yl (E, E)-hepta-2,4-dienoate.
Biphenyl-4-yl (E, E)-octa-2,4-dienoate.
4'-Propylbiphenyl-4-yl (E, E)-hexa-2,4-dienoate.
4'-Pentylbiphenyl-4-yl (E, E)-hexa-2,4-dienoate, K 86.degree. C.,
N-I 168.degree. C.
4'-Heptylbiphenyl-4-yl (E, E)-hexa-2,4-dienoate.
4'-Propyloxybiphenyl-4-yl (E, E)-hexa-2,4-dienoate.
4'-Butyloxybiphenyl4-yl (E, E)-hexa-2.4-dienoate.
4'-Pentyloxybiphenyl-4-yl (E, E)-hexa-2,4-dienoate.
4'-Hexyloxybiphenyl-4-y(E, E)-hexa-2,4-dienoate.
4'-Heptyloxybiphenyl-4-yl (E, E)-hexa-2,4-dienoate.
4'-Octyloxybiphenyl-4-yl (E, E)-hexa-2,4-dienoate.
4'-(Trifluoromethoxy)biphenyl4-yl (E, E)-hexa-2,4-dienoate.
4'-(Trifluoroaceto)biphenyl4-yl (E, E)-hexa-2,4-dienoate.
4'-Fluorobiphenyl-4-yl (E, E)-hexa-2,4-dienoate.
3',4'-Difluorobiphenyl-4-yl (E, E)-hexa-2,4-dienoate.
3',4',5'-Trifluorobiphenyl-4-yl (E, E)-hexa-2,4-dienoate.
trans-4-Cyanocyclohexyl (E, E)-hepta-2,4-dienoate.
trans-4-Cyanocyclohexyl (E, E)-octa-2,4ienoate.
trans-4-(4'-Cyanophenyl)cyclohexyl (E, E)-hexa-2,4-dienoate.
trans-4-(4'-Fluorophenyl)cyclohexyl (E, E)-hexa-2,4-dienoate.
trans-4-(4'-Trifluoromethoxyphenyl)cyclohexyl (E,
E)-hexa-2,4-dienoate.
trans-4-(4'-Trifluoroacetophenyl)cyclohexyl (E,
E)-hexa-2,4-dienoate.
4-(trans-4-Cyanocyclohexyl)phenyl (E, E)-hexa-2,4-dienoate.
trans-4-(trans-4-Cyanocyclohexyl)cyclohexyl (E,
E)-hexa-2,4-dienoate.
4-(trans-4-Pentylcyclohexyl)phenyl (E, E)-hexa-2,4-dienoate, K
86.degree. C., N-I 172.degree. C.
trans-4-(trans-4-Propylcyclohexyl)cyclohexyl (E,
E)-hexa-2,4-dienoate.
trans-4-(trans-4-Pentylcyclohexyl)cyclohexyl (E,
E)-hexa-2,4-dienoate, K 117.degree. C., N-I 180.degree.C.
trans-4-(trans-4-Heptylcyclohexyl)cyclohexyl (E,
E)-hexa-2,4-dienoate.
trans-4-(trans-4-Propylcyclohexyl)cyclohexyl (E, E)-hepta-2
,4dienoate.
trans-4-(trans-4-Pentylcyclohexyl)cyclohexyl (E,
E)-hepta-2,4-dienoate.
trans-4-(trans-4-Heptylcyclohexyl)cyclohexyl (E,
E)-hepta-2,4-dienoate.
trans-4-(trans-4-Propylcyclohexyl)cyclohexyl (E,
E)-octa-2,4-dienoate.
trans-4-(trans-4-Pentylcyclohexyl)cyclohexyl (E,
E)-octa-2,4-dienoate.
trans-4-(trans-4-Heptylcyclohexyl)cyclohexyl (E,
E)-octa-2,4-dienoate.
t-(trans-4-Propylcyclohexyl)phenyl (E, E)-hexa-2,4-dienoate.
4-(trans-4-Heptylcyclohexyl)phenyl (E, E)-hexa-2,4-dienoate.
4-(trans-4-Propylcyclohexyl)phenyl (E, E)-hepta-2,4-dienoate.
4-(trans-4-Pentylcyclohexyl)phenyl (E, E)-hepta-2,4-dienoate.
4-(trans-4-Heptylcyclohexyl)phenyl (E, E)-hepta-2,4-dienoate.
4-(trans-4-Propylcyclohexyl)phenyl (E, E)-octa-2,4-dienoate.
4-(trans-4-Pentylcyclohexyl)phenyl (E, E)-octa-2,4-dienoate.
4-(trans-4-Heptylcyclohexyl)phenyl (E, E)-octa-2,4-dienoate.
4-(5-Pentylpyrimidin-2-yl)phenyl (E, E)-hexa-2,4-dienoate.
4-(2-Pentylpyridin-5-yl)phenyl (E, E)-hexa-2,4-dienoate.
4-(5-Cyanopyridin-2-yl)phenyl (E, E)-hexa-2,4-dienoate.
4-(2-Cyanopyridin-5-yl)phenyl (E, E)-hexa-2,4-dienoate.
4-(5-Pentylpyridin-2-yl)phenyl (E, E)-hexa-2,4-dienoate.
4-(2-Pentylpyridin-5-yl)phenyl (E, E)-hexa-2,4-dienoate.
4-(5-Cyanopyridin-2-yl)phenyl (E, E)-hexa-2,4-dienoate.
4-(2-Cyanopyridin-5-yl)phenyl (E, E)-hexa-2,4-dienoate.
5-(4-Pentylphenyl)pyrimidin-2-yl (E, E)-hexa-2,4-dienoate.
2-(4-Pentylphenyl)pyrimidin-5-yl (E, E)-hexa-2,4-dienoate.
5-(4-Cyanophenyl)pyrimidin-2-yl (E, E)-hexa-2,4-dienoate.
2-(4-Cyanophenyl)pyrimidin-5-yl (E, E)-hexa-2,4-dienoate.
5-(4-Pentylphenyl)pyridin-2-yl (E, E)-hexa-2,4-dienoate.
2-(4-Pentylphenyl)pyridin-5-yl (E, E)-hexa-2,4-dienoate.
5-(4-Cyanophenyl)pyridin-2-yl (E, E)-hexa-2,4-dienoate.
2-(4-Cyanophenyl)pyridin-5-yl (E, E)-hexa-2,4-dienoate.
4-[(E, E)-hexa-2,4-dienoyloxy]phenyl (E, E)-hexa-2,4-dienoate, K
183.degree. C., N-I 186.degree. C.
4-[(E, E)-hepta-2,4-dienoyloxy]phenyl (E,
E)-hepta-2,4-dienoate.
[(E, E)-octa-2,4-dienoyloxy]phenyl (E, E)-octa-2,4-dienoate.
4-(5-Cyanothophen-2-yl)phenyl (E,E)-hexa-2,4-dienoate, K
168.degree. C., N-I 188.degree. C.
4-(5-Pentylthophen-2-yl)phenyl (E,E)-hexa-2,4-dienoate, K
76.degree. C., N-I 125.degree. C.
EXAMPLE 3
Preparation of trans-, trans-4-(E,
E)-hexa-2,4-dienyloxy4'-pentyl-1, 1'-bicyclohexane
A mixture of toluene-4-sulfonic acid (E, E)-hexa-2,4-dienyl ester
(1.0 g, 4.0 mmol), trans-, trans-4-hydroxy-4'-pentyl-1,
1'-bicyclohexane (0.37 g, 1.5 mmol), potassium tert-butoxide (0.55
g, 4.5 mrnol) and 1,2-dimethoxyethane (20 cm.sup.3) is stirred at
room temperature overnight, filtered to remove inorganic material,
diluted with water (100 cm.sup.3) and then extracted into diethyl
ether (3.times.25 cm.sup.3). The combined organic extracts are
washed with water (2.times.200 cm.sup.3), dried (MgSO.sub.4),
filtered and then evaporated down. The residue is purified by
column chromatography on silica gel using a 9:1 hexane/ethyl
acetate mixture as eluent and recrystallisation from ethanol to
yield 0.25 g (51%) of the desired ether.
The toluene-4-sulfonic acid (E, E)-hexa-2,4-dienyl ester requirets
starting material could be prepared as follows:
A solution of toluene4-sulfonyl chloride (0.75 g, 4.0 mmol) in
dichloromethane (10 cm.sup.3) is added slowly to a solution of (E,
E)-hexa-2,4-dienol (0.40 g, 4.0 mmol), triethylamine (0.80 g, 8.0
mmol) and dichloromethane (50 cm.sup.3) at 0.degree. C. The
reaction mixture is stirred at 0.degree. C. for 6 h, washed with
dilute hydrochloric acid (2.times.50 cm.sup.3), water (2.times.50
cm.sup.3) and dilute sodium carbonate solution (2.times.50
cm.sup.3), dried (MgSO4), filtered and then evaporated down to
yield 1.0 g (99%) of the desired tosylate, which is used without
further purification.
The following compounds could be obtained analogously:
trans-, trans-4-[(E,
E)-Hexa-2,4-dienyloxy]-4'-propyl-1,1'-bicyclohexane.
trans-, trans-4-[(E,
E)-Hexa-2,4-dienyloxy]-4'-pentyl-1,1'-bicyclohexane.
trans-, trans-4-[(E, E)-Hexa-2,4-dienyloxy]-4'-heptyl-1,1
'-bicyclohexane.
trans-, trans-4-[(E,
E)-Hepta-2,4-dienyloxy]-4'-propyl-1,1'-bicyclohexane.
trans-, trans-4-[(E,
E)-Hepta-2,4-dienyloxy]-4'-pentyl-1,1'-bicyclohexane.
trans-, trans-4-[(E,
E)-Hepta-2,4-dienyloxy]-4'-heptyl-1,1'-bicyclohexane.
trans-, trans-4-[(E,
E)-Octa-2,4-dienyloxy]-4'-propyl-1,1'-bicyclohexane.
trans-, trans-4-[(E,
E)-Octa-2,4-dienyloxy]-4'-pentyl-1,1'-bicyclohexane.
trans-, trans-4-[(E,
E)-Octa-2,4-dienyloxy]-4'-heptyl-1,1'-bicyclohexane.
trans-1-[(E, E)-Hexa-2,4-dienyloxy]-4-propylcyclohexane.
trans-1-[(E, E)-Hexa-2,4-dienyloxy]-4-pentylcyclohexane.
trans-1-[(E, E)-Hexa-2,4-dienyloxy]-4-heptylcyclohexane.
trans-, trans-4,4'-di-[(E,
E)-Hexa-2,4-dienyloxy]-1,1'-bicyclohexane.
trans-, trans-4,4'-di-[(E,
E)-Hepta-2,4-dienyloxy]-1,1'-bicyclohexane .
trans-, trans-4,4'-di-[(E,
E)-Octa-2,4-dienyloxy]-1,1'-bicyclohexane.
trans-, 4-[-((E, E)-Hexa-2,4-dienyloxy]cycloxhexane.
trans-4,4 'di-[(E, E)-Hepta-2,4-dienyloxy]cyclohexane.
trans-1, 4di-[(E, E)-Octa-2,4-dienyloxy]cyclohexane.
4-(trans-4-[E, E)-Hexa-2,4-dienyloxy]cyclohexyl)benzonitrile.
4-(trans-4-[E, E)-Hepta-2,4-dienyloxy]cyclohexyl)benzonitrile.
4-(trans-4-[E, E)-Octa-2,4-dienyloxy]cyclohexyl)benzonitrile.
1-Fluoro-4-(trans-4-[E,
E)-hexa-2,4-dienyloxy]cyclohexyl)benzene.
1-Chloro-4-(trans-4-[E,
E)-hexa-2,4-dienyloxy]cyclohexyl)benzene.
1-Bromo-4-(trans-4-[E,
E)-hexa-2,4-dienyloxy]cyclohexyl)benzene.
1,2-Difluoro-4-(trans-4-[E,
E)-hexa-2,4-dienyloxy]cyclohexyl)benzene.
1,2,6-Trifluoro-4-(trans-4-[E,
E)-hexa-2,4-dienyloxy]cyclohexyl)benzene.
1-Trifluoromethoxy-4-(trans-4-[E,
E)-hexa-2,4-dienyloxy]cyclohexyl)benzene.
1-Trifluoromethyl-4-(trans-4-[E,
E)-hexa-2,4dienyloxy]cyclohexyl)benzene.
1-Trifluoroaceto-4-(trans-4-[E,
E)-hexa-2,4-dienyloxy]cyclohexyl)benzene.
1-Propyl-4-(trans-4-[E,
E)-hexa-2,4dienyloxy]cyclohexyl)benzene.
1-Pentyl-4-(trans-4-[E,
E)-hexa-2,4-dienyloxy]cyclohexyl)benzene.
1-Heptyl-4-(trans-4-[E,
E)-hexa-2,4-dienyloxy]cyclohexyl)benzene.
1-Methoxy-4-(trans-4-[E,
E)-hexa-2,4-dienyloxy]cyclohexyl)benzene.
1-Ethoxy-4-(trans-4-[E,
E)-hexa-2,4-dienyloxy]cyclohexyl)benzene.
1-Proxy-4-(trans-4-[E, E)-hexa-2,4-dienyloxy]cycohexyl)benzene.
1-Butoxy-4-(trans-4-[E,
E)-hexa-2,4-dienyloxy]cyclohexyl)benzene.
1-Pentyloxy-4-(trans-4-[E,
E)-hexa-2,4-dienyloxy]cyclohexyl)benzene.
1-Hexyloxy-4-(trans-4-[E,
E)-hexa-2,4-dienyloxy]cyclohexyl)benzene.
1-Heptyloxy-4-(trans-4-[E,
E)-hexa-2,4-dienyloxy]cyclohexyl)benzene.
1-Octyloxy-4-(trans-4-[E,
E)-hexa-2,4-dienyloxy]cyclohexyl)benzene.
4-Cyano-4'-(trans-4-[E,
E)-hexa-2,4-dienyloxy]cyclohexyl)biphenyl.
4-Fluoro-4-(trans 4-[E,
E)-hexa-2,4-dienyloxy]cyclohexyl)biphenyl.
4-Chloro-4'-(trans-4-[E,
E)-hexa-2,4-dienyloxy]cyclohexyl)biphenyl.
4-Bromo-4'-(trans-4-[E,
E)-hexa-2,4-dienyloxy~cyclohexyl)biphenyl.
4-Trifluoromethoxy-4'-(trans-4-[E,
E)-hexa-2,4dienyloxy]cyclohexyl)biphenyl.
4-Trifluoromethyl-4'-(trans-4-[E,
E)-hexa-2,4dienyloxy]cyclohexyl)biphenyl.
4-Propyl-4'-(trans-4-[E,
E)-hexa-2,4-dienyloxy]cyclohexyl)biphenyl.
4-Pentyl-4'-(trans-4-[E,
E)-hexa-2,4-dienyloxy]cyclohexyl)biphenyl.
4-Heptyl-4'-(trans-4-4E,
E)-hexa-2,4dienyoxy]cyclohexyl)bipheyenyl.
4-Methoxy-4'-(trans-4-[E,
E)-hexa-2,4-dienyloxy]cyclohexyl)biphenyl.
4-Ethoxy-4'-(trans-4-[E,
E)-hexa-2,4-dienyloxy]cyclohexyl)biphenyl.
4-Propoxy-4'-(trans-4-[E,
E)-hexa-2,4-dienyloxy]cyclohexyl)biphenyl.
4-Butoxy-4'-(trans-4-[E,
E)-hexa-2,4-dienyloxy]cyclohexyl)biphenyl.
4-Pentyloxy-4'-(trans-4-[E,
E)-hexa-2,4-dienyloxy]cyclohexyl)biphenyl.
4-Hexyloxy-4'-(trans-4-[E,
E)-hexa-2,4-dienyloxy]cyclohexyl)biphehyl.
4-Heptyoxy-4'-(trans-4-[E,
E)-hexa-2,4-dienyloxy]cyclohexyl)biphenyl.
4-[trans-4-(trans-4-[(E,
E)-Hexa-2,4-dienyloxy]cyclohexyl)cyclohexyl]benzonitrile.
1-Fluoro-4-[trans-4-(trans-[(E,
E)-hexa-2,4-dienyloxy]cyclohexyl)cyclohexyl]benzene.
1-Chloro-4-[trans-4-(trans-4-[(E,
E)-hexa-2,4-dienyloxy]cyclohexy]cyclohexyl)benzene.
1-Chomro-4-[trans-4-(trans-4-[(E,
E)-hexa-2,4-dienyloxy]cyclohexyl]cyclohexyl)benzene.
1-Trifluoromethoxy-4-[trans-4-(trans-4-[(E,
E)-hexa-2,4-dienyloxy]cyclohexyl)cyclohexyl]benzene.
1-Trifluoromethyl-4-[trans-4-(trans-4-[(E,
E)-hexa-2,4-dienyloxy]cyclohexyl)cyclohexyl]benzene.
1-Trifluoroaceto-4-[trans-4-(trans-4-[(E,
E)-hexa-2,4-dienyloxy]cyclohexyl)cyclohexyl]benzene.
4-(trans-5-[E, E)-Hexa-2,4-dienyloxy]dioxan-2-yl)benzonitrile.
4-(trans-5-[E, E)-Hepta-2,4-dienyloxy]dioxan-2-yl)benzonitrile.
4-(trans-5-[E, E)-Octa-2,4-dienyloxy]dioxan-2-yl)benzonitrile.
1-Fluoro-4-(trans-5-[E,
E)-hexa-2,4-dienyloxyl]dioxan-2-yl)benzene.
1-Chloro-4-(trans-5-[E,
E)-hexa-2,4dienyloxy]dioxan-2-yl)benzene.
1-Bromo-4-(trans-5-[E,
E)-hexa-2,4-dienyloxy]dioxan-2-yl)benzene.
1,2-Difluoro-4-(trans-5-[E,
E)-hexa-2-dienyloxy-]dioxan-2-yl)benzene.
1,2,6-Trifluoro-4-(trans-5-[E,
E)-hexa-2,4dienyloxyl]dioxan-2-yl)benzene.
1-Trifluoromethoxy-4-(trans -5-[E,
E)-hexa-2,4-dienyloxy]dioxan-2-yl)benzene.
1-Trifluoromethyl-4-(trans-5-[E,
E)-hexa-2,4dienyloxyl]dioxan-2-yl)benzene.
1-Trifluoroaceto-4-(trans-5-[E,
E)-hexa-2,4dienyloxy]dioxan-2-yl)benzene.
1-Propyl-4-(trans-5-[E,
E)-hexa-2,4dienyloxy]dioxan-2-yl)benzene.
1-Pentyl-(trans-5-[E,
E)-hexa-2,4-dienyloxy]dioxan-2-yl)benzene.
1-Heptyl-4-(trans-5-[E,
E)-hexa-2,4dienyloxyl]dioxan-2-yl)benzene.
1-Methoxy-4-(trans-5-[E,
E)-hexa-2,4dienyloxy]dioxan-2-yl)benzene.
1-Ethoxy-4-(trans-5-[E,
E)-hexa-2,4-dienyloxy]dioxan-2-yl)benzene.
1-Proxy-4-(trans-5-[E,
E)-hexa-2,4-dienyloxy]dioxan-2-yl)benzene.
1-Butxyl-4-(trans-5-[E,
E)-hexa-2,4-dienyloxy]dioxan-2-yl)benzene.
1-Pentyloxy-4-(trans-5-[E,
E)-hexa-2,4-dienyloxy]dioxan-2-yl)benzene.
1-Hexyloxy-4-(trans-5-[E,
E)-hexa-2,4-dienyloxy]dioxan-2-yl)benzene.
1-Heptyloxy-4-(trans-5-[E,
E)-hexa-2,4-dienyloxy]dioxan-2-yl)benzene.
1-Octyloxy-4-(trans-5-[E,
E)-hexa-2,4-dienyloxy]dioxan-2-yl)benzene.
1-Cyano-4'-(trans-5-[E,
E)-hexa-2,4-dienyloxy]dioxan-2-yl)biphenyl.
4-Fluoro-4'-(trans-5-[E,
E)-hexa-2,4-dienyloxy]dioxan-2-yl)biphenyl.
4-Chloro-4'-(trans-5-[E,
E)-hexa-2,4-dienyloxy]dioxan-2-yl)biphenyl.
4-Bromo-4'-(trans-5-[E,
E)-hexa-2,4-dienyloxy]dioxan-2-yl)biphenyl.
4-Trifluoromethoxy-4'-(trans-5-[E,
E)-hexa-2,4-dienyloxy]dioxan-2-yl)biphenyl.
4-Trifluoromethyl-4'-(trans-5-[E,
E)-hexa-2,4-dienyloxy]dioxan-2-yl)biphenyl.
4-Propyl-4'-(trans-5-[E,
E)-hexa-2,4-dienyloxy]dioxan-2-yl)biphenyl.
4-Pentyl-4'-(trans-5-[E, E)-hexa-2,4-dienyloxy]dioxan-2-yl
l)biphenyl.
4-Heptyl-4'-(trans-5-[E,
E)-hexa-2,4dienyloxy]dioxan-2-yl)biphenyl.
4-Methoxy-4'-(trans-5-[E,
E)-hexa-2,4dienyloxy]dioxan-2-yl)biphenyl.
4-Ethoxy-4'-(trans-5-[E,
E)-hexa-2,4-dienyloxy]dioxan-2-yl)biphenyl.
4-Propoxy-4'-(trans-5-[E,
E)-hexa-2,4-dienyloxy]dioxan-2-yl)biphenyl.
4-Butoxy-4'-(trans-5-[E,
E)-hexa-2,4-dienyloxy]dioxan-2-yl)biphenyl.
4-Pentyloxy-4'-(trans-5-[E,
E)-hexa-2,4-dienyloxy]dioxan-2-yl)biphenyl.
4-Hexyloxy-4'-(trans-5-[E,
E)-hexa-2,4-dienyloxy)]dioxan-2-yl)biphenyl.
4-Heptyloxy4'-(trans-5-[E,
E)-hexa-2,4-dienyloxy]dioxan-2-yl)biphenyl.
4-[trans-4-(trans-5-[(E,
E)-Hexa-2,4-dienyloxy]dioxan-2-yl)cyclohexyl]benzonitrile.
TABLE 1 Transition temperatures for the compounds below: ##STR4##
Compound R C-N/.degree. C. N-I/.degree. C. .DELTA.T.sub.NI
/.degree. C. ##STR5## 58 77 19 ##STR6## 74 82 8 ##STR7## 74 81 7
##STR8## 125 152 27
TABLE 2 Transition temperatures for the compounds below: ##STR9##
Compound R C-N/.degree. C. N-I/.degree. C. .DELTA.T.sub.NI
/.degree. C. ##STR10## 53 71 18 ##STR11## 92 131 39 ##STR12## 97
(74) -- ##STR13## 160 227 67
TABLE 3 Transition temperatures for the compounds below ##STR14##
Compound X C-N/.degree. C. S.sub.A -N/.degree. C. N-I/.degree. C.
.DELTA.T.sub.NI /.degree. C. H 110 (84) (92) -- CN 160 227 67 ( )
Represents a monotropic transition temperature
( ) Represents a monotropic transition temperature
TABLE 4 Transition temperatures for the compounds below ##STR15##
Compound X C-N/I .degree. C. N-I/.degree. C. .DELTA.T.sub.NI
/.degree. C. ##STR16## 111 -- -- ##STR17## 116 141 27 ##STR18## 160
227 67
TABLE 5 Transition temperatures for the compounds below ##STR19##
Compound Z.sub.1 Z.sub.2 C-N/I/.degree. C. N-I .DELTA.T.sub.NI
/.degree. C. OOC COO 86 -- -- COO OOC 183 186 3
TABLE 6 Transition temperatures for the compounds ##STR20##
Compound R C-N/.degree. C. N-I/.degree. C. ##STR21## 86 172
##STR22## 117 180
The following birefringence data was obtained: ##STR23##
Wt/% in ZLI3086=5
Ext .DELTA.n 30.degree. C.=0.328
Ext .DELTA.n 20.degree. C.=0.333
Ext .DELTA.n T/T.sub.NI =0.8=0.298
wherein Ext .DELTA.n is a linar extrapolation in concentration of
the birefringence in ZLI3086 which is a commercially available
(from Merck UK) apolar nematic host mixture. T is the temperature
at which the measurement was taken (in Kelvin) and T.sub.NI is the
phase transition for the nematic-isotropic phase change (in
Kelvin).
One known device in which the materials of the current invention
may be incorporated is the twisted nematic device which uses a thin
layer of a nematic material between glass slides. The slides are
unidirectionally rubbed and assembled with the rubbing directions
orthogonal. The rubbing gives a surface alignment to the liquid
crystal molecules resulting in a progressive 90.degree. twist
across the layer. When placed between polarisers, with their
optical axis perpendicular or parallel to a rubbing direction the
device rotates the plane of polarised light in its OFF state and
transmits without rotation in the ON state. Small amounts of
cholesteric material may be added to the nematic material to ensure
the 90.degree. twist is of the same sense across the whole area of
the device as explained in UK patents 1,472,247 and 1,478,592.
An improvement in the performance of large, complex, nematic LCDs
occurred in 1982 when it was observed that the voltage dependence
of the transmission of nematic LC layers with twist angles in the
range 180.degree. to 270.degree. could become infinitely steep, see
C. M. Waters, V. Brimmell and E. P. Raynes, Proc. 3rd Int. Display
Res. Conf., Kobe, Japan, 1983, 396. The largertwist angles are
produced by a combination of surface alignment and making the
nematic mixture into a long pitch cholesteric by the addition of a
small amount of a chiral twisting agent. The increasing twist angle
steepens the transmission/voltage curve, until it becomes bistable
for 270.degree. twist; for a specific twist angle between
225.degree. and 270.degree. the curve becomes infinitely steep and
well suited to multiplexing. The larger twist angles present have
resulted in the name supertwisted nematic (STN) for these LCDs.
Liquid Crystal Devices describing the use of STNs may be found in
patent application GB 8218821 and resulting granted patents
including U.S. Pat. No. 4,596,446.
The display of FIGS. 1 and 2 comprises a liquid crystal cell 1
formed by a layer 2 of cholesteric liquid crystal material
contained between glass walls 3,4. A spacer ring 5 maintains the
walls typically 6 .mu.m apart. Strip like row electrodes 6.sub.1 to
6.sub.m, e.g. of SnO.sub.2 are formed on one wall 3 and similar
column electrodes 7.sub.1 to 7.sub.n formed on the other wall 4.
With m-row electrodes and n-column electrodes this forms an mxn
matrix of addressable elements. Each element is formed by the
interaction of a row and column electrode.
A row driver supplies voltage to each row electrode 6. Similarly a
column drive 9 supplies voltages to each column electrode 7.
Control of applied voltages is from a control logic 10 which
receives power from a voltage source 11 and timing from a clock
12.
An example of the use of a material and device embodying the
present invention will now be described with reference to FIG.
2.
The liquid crystal device consists of two transparent plates, 3 and
4, for example made from glass. These plates are coated on their
internal face with transparent conducting electrodes 6 and 7. An
alignment layer is introduced onto the internal faces of the cell
so that a planar orientation of the molecules making up the liquid
crystalline material will be approximately parallel to the glass
plates 3 and 4. This is done by coating the glass plates 3,4
complete with conducting electrodes so that the intersections
between each column and row form an x, y matrix of addressable
elements or pixels. For some types of display the alignment
directions are orthogonal. Prior to the construction of the cell
the alignment layers are rubbed with a roller covered in cloth (for
example made from velvet) in a given direction, the rubbing
directions being arranged parallel (same or opposite direction)
upon construction of the cell. A spacer 5 e.g. of polymethyl
methacrylate separates the glass plates 3 and 4 to a suitable
distance e.g. 2 microns. Liquid crystal material 2 is introduced
between glass plates 3,4 by filling the space in between them. This
may be done by flow filling the cell using standard techniques. The
spacer 5 is sealed with an adhesive in a vacuum using an existing
technique. Polarisers 13 may be arranged in front of and behind the
cell.
Alignment layers may be introduced onto one or more of the cell
walls by one or more of the standard surface treatment techniques
such as rubbing, oblique evaporation or as described above by the
use of polymer aligning layers.
In alternative embodiments the substrates with the aligning layers
on them are heated and sheared to induce alignment, alternatively
the substrates with the aligning layers are thermally annealed
above the glass transition temperature and below the liquid crystal
to isotropic phase transition in combination with an applied field.
Further embodiments may involve a combination of these aligning
techniques. With some of these combinations an alignment layer may
not be necessary.
The device may operate in a transmissive or reflective mode. In the
former, light passing through the device, e.g. from a tungsten
bulb, is selectively transmitted or blocked to form the desired
display. In the reflective mode a mirror, or diffuse reflector,
(16) is placed behind the second polariser 13 to reflect ambient
light back through the cell and two polarisers. By making the
mirror partly reflecting the device may be operated both in a
transmissive and reflective mode.
The alignment layers have two functions, one to align contacting
liquid crystal molecules in a preferred direction and the other to
give a tilt to these molecules--a so called surface tilt--of a few
degrees typically around 4.degree. or 5.degree.. The alignment
layers may be formed by placing a few drops of the polyimide on to
the cell wall and spinning the wall until a uniform thickness is
obtained. The polyimide is then cured by heating to a predetermined
temperature for a predetermined time followed by unidirectional
rubbing with a roller coated with a nylon cloth.
In an alternative embodiment a single polariser and dye material
may be combined.
Cholesteric or chiral nematic liquid crystals possess a twisted
helical structure which is capable of responding to a temperature
change through a change in the helical pitch length. Therefore as
the temperature is changed then the wavelength of the light
reflected from the planar cholesteric structure will change and if
the reflected light covers the visible range then distinct changes
in colour occur as the temperature varies. This means that there
are many possible applications including the areas of thermography
and thermooptics.
The cholesteric mesophase differs from the nematic phase in that in
the cholesteric phase the director is not constant in space but
undergoes a helical distortion. The pitch length for the helix is a
measure of the distance for the director to turn through 3600.
By definition, a cholesteric material is chiral material.
Cholesteric materials may also be used in electro-optical displays
as dopants, for example in twisted nematic displays where they may
be used to remove reverse twist defects, they may also be used in
cholesteric to nematic dyed phase change displays where they may be
used to enhance contrast by preventing waveguiding.
Thermochromic applications of cholesteric liquid crystal materials
usually use thin film preparations of the cholesterogen which are
then viewed against a black background. These temperature sensing
devices may be placed into a number of applications involving
thermometry, medical thermography, non-destructive testing,
radiation sensing and for decorative purposes. Examples of these
may be found in D G McDonnell in Thermotropic Liquid Crystals,
Critical Reports on Applied Chemistry, Vol 22, edited by G W Gray,
1987 pp 120-44; this reference also contains a general description
of thermochromic cholesteric liquid crystals.
Generally, commercial thermochromic applications require the
formulation of mixtures which possess low melting points, short
pitch lengths and smectic transitions just below the required
temperature-sensing region. Preferably the mixture or material
should retain a low melting point and high smectic-cholesteric
transition temperatures.
In general, thermochromic liquid crystal devices have a thin film
of cholesterogen sandwiched between a transparent supporting
substrate and a black absorbing layer. One of the fabrication
methods involves producing an `ink` with the liquid crystal by
encapsulating it in a polymer and using printing technologies to
apply it to the supporting substrate. Methods of manufacturing the
inks include gelatin microencapsulation, U.S. Pat. No. 3,585,318
and polymer dispersion, U.S. Pat. Nos. 1,161,039 and 3,872,050. One
of the ways for preparing well-aligned thin-film structures of
cholesteric liquid crystals involves laminating the liquid crystal
between two embossed plastic sheets. This technique is described in
UK patent 2,143,323.
For a review of thermochromism in liquid crystals see J G Grabmaier
in `Applications of Liquid Crystals`, G Meier, E Sackmann and J G
Grabmaier, Springer-Veriag, Berlin and New York, 1975, pp
83-158.
The materials of the current invention may be used in many of the
known devices including those mentioned in the introduction.
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